Temperature control devices utilizing thermal sensing elements are commonly used in the industry, i.e., in applications where temperature of a certain environment is to be kept within a desirable range. These applications occur in a variety of media such as gases, liquids, or solids in which temperature control is desired.
One of the commonly seen applications is the temperature control of an environmental chamber. In such an application, a temperature control device is utilized where a thermal sensing element is exposed to the interior of the chamber. The thermal sensing element senses the temperature changes in the chamber and sends back either a mechanical or electrical signal to the temperature control device which in turn, either turns on or turns off the heating element in the chamber.
There are many different types of thermal sensing elements in existence today. These include the bimetallic type, where two strips of metal each of a different thermal expansion characteristic are laminated together. A temperature change causes the laminated bimetallic strip to bend toward an electrical contact thus activating the temperature control device. Another type of commonly used thermal sensing element is a tubular casing containing a thermal responsive material and a triggering element. A commonly used heat responsive material in this type of thermal sensing element is a petroleum based wax which expands or contracts according to temperature changes. A triggering device is activated by the volume change of the wax material to send out signals to the temperature control device.
A common drawback of these two types of thermal sensing elements is their limitation in temperature sensitivity. the coefficients of thermal expansion of these materials are not very high. As a result, these thermal sensing elements are not very useful when the device is to respond to a small temperature change. Another drawback in the application of these thermal sensing elements is that a relatively large volume of material must be used in order to produce the necessary volume change in them to trigger the temperature control device. This leads to rather bulky thermal sensing elements which may not be practical for applications where space is limited.
It is therefore an object of the present invention to provide a thermal sensing element containing a heat responsive material having a very high negative coefficient of thermal expansion.
It is yet another object of the present invention to provide a thermal sensing element containing an elastomeric heat responsive material that is sensitive enough to detect minute temperature changes.
It is a further object of the present invention to provide a thermal sensing element containing a heat responsive elastomeric material that shrinks appreciably with relatively small temperature increases and can also be packaged in a compact container for use in applications where space is limited.